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JAKE SMITH |
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Not too long ago I addressed the use of ‘on-demand’ water heaters and the use of thermo-static valves. Considering that the systems being offered are being specified with more luxury types of installations, we have tried to provide information in the price book and in the instruction manual to help installers put the correct pieces into place for the correct installation. A heating and plumbing specialist will have more information for the people interested in details. However, for a general review, read on.
The 2006 ROHL Price Book has a thermostatic shower system review in each section of the collections. Our recommendation for water heaters is as follows:
“A 100 gallon water heater
is recommended as a minimum. For an ‘on-demand’ water system, we recommend a 25-gallon standard water heater plumbed in line for consistent water temperature. Consult a professional!”
As a word of explanation, thermostatic valves deliver up to twice as many gallons per minute than a pressure balance valve. If that demand
is 16 gallons per minute, when you mix hot water to cold water, it is a 70% hot water to a 30% cold water mix. That equals 11.2 gallons per minute of hot water. That’s a lot of water.
A 50-gallon water heater on a straight demand would only have water for 4 minutes and 45 seconds.
Most systems do not have a full 16 GPM flow.
Showerheads are restricted
to 2.5 GPM, but even with the restrictor out, it may only have 5 to 6 GPM flow.
The more you add on, the more water is used. You
do have to calculate what your average usage will be
at the peak times during the day. Generally, that is weekday mornings.
‘On-demand’ systems have different delivery outputs. Simply put, if the hot water demand from a shower system out paces the delivery of the ‘on-demand’ water system, it will feel like you are running out of hot water. Referring to advice from professionals, we put into our ROHL Price Book that a 25-gallon standard water heater installed in line with the ‘on demand’ heater will help ensure that there will be a constant flow of hot water. The thermostatic valve draws water from the water heater, and the ‘on-demand’ system delivers it to the water heater.
On a technical call to Takagi, and giving
the parameters of 5000 sq ft house, with a demand from the valve at 11 GPM of hot water, the technician recommends 2 of the model number T-M1 installed in line. Each unit delivers 5 GPM and up to 300 gallons per hour. Take time to calculate the usage with all the showers running.
We have also heard that a re-circulating line is absolutely necessary for instant delivery of hot water. And the water heater should be set at 135 to 140 degrees Fahrenheit.
‘On-demand’ systems are here to stay. The units save space and money, and if installed with the correct rating and the other recommendations listed above, will work correctly in a luxury application.
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Irvine, California 92618 
